Gun perforators for wells



June 12, 1956 E. BABCOCK 2,749,840

cuu PERFORATORS FOR WELLS Filed Sept. 11. 1950 39 o FIRING CAP POWDER PRIMA A? com) a will I .l

4 II II FILLED WITH INERT MATERIAL H. FIG. 2.

United States Patent 2,749,840 Patented June 12, 1956 GUN PERFORATORS FOR WELLS Earl Babcock, Houston, Tex., assiguor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N. J., a corporation of Delaware Application September 11, 1950, Serial No. 184,166

2 Claims. (Cl. 102-20) This invention relates to guns for perforating casing in oil wells or the like and more particularly to guns which use shaped charges of explosive to perforate casing with jet action.

Methods of perforating casing in oil wells with charges of explosive which utilize the Monroe effect are now common. Guns constructed for this purpose ordinarily consist of a steel housing or carrier which is provided with a number of ports in which the charges of explosive are individually mounted and sealed. Since the carrier is ordinarily hollow and the interior kept free from liquid contamination as the gun is lowered through mud or the like in the well bore, it must be built strong enough, and each seal must be strong enough, to withstand the high fluid pressure encountered in deep wells. The cost of such carriages and the expense involved in re-loading them is high.

Expendible carriages, such as those made of cardboard, various plastics or the like are proposed in the patent to Davis and Burrows No. 2,399,211, but these have not come into general use perhaps because of the inability of such materials to withstand high bottom hole pressures.

Carriages of solid concrete have also been proposed and these have been commercially used, but are thought by some people skilled in the art to be undesirable because of their tendency to burst the casing.

In accordance with the present invention it is proposed to make a carriage for jet perforator guns of a thin expendible outer tubular container which completely surrounds the charges of explosives and seals them from fluid in the well bore. The charges are merely placed in the container so that expensive individual seals are not required. Instead of trying to re-load such a container after it has once been used, it is proposed merely to throw it away or sell it for junk, the initial cost being kept to a minimum.

Since such a thin container is incapable of confining forces of the explosion to any great extent or of withstanding high bottom hole pressure, the charges themselves are enclosed in sealed pressure resistant envelopes and the spaces in the container between the charges of explosive are filled with inert filling material. With such material inside the container, the mass of the gun assembly is increased. Hence it will sink through heavy fluid in the well bore. Another purpose in providing considerable mass is to dissipate the radial explosive eifects of the shaped charges in directions other than the direction of the jet. By providing a quantity of heavy, more or less unconfined, granular or loose material, the explosive surge is scattered due to inertia of the particles and, without resorting to a strong housing, the tendency of the explosion to burst the casing is minimized.

Another advantage in the use of a thin tubular container for the charges of explosives is that it permits of a construction having a certain amount of flexibility. Perforating gun carriers heretofore proposed, whether they be of steel, concrete or plastic have been rigid. It is well known that pipe in well bores is often not straight, and

that carriers, since they are of elongated shape cannot be lowered into a well bore unless they are of a diameter materially less than the internal diameter of the pipe through which they must pass, or unless the pipe is unusually straight.

Of particular significance in this connection is the fact that it has recently been proposed to lower perforating guns through tubing inside the casing in an oil well. See for example the application of Theodore A. Huber, Serial No. 133,025, filed December 15, 1949, for Method of Completing and Repairing Oil Wells where the use of a casing perforating gun capable of being run through tubing is required. Large savings in time and cost in drilling can be effected in this way if effective perforation can be accomplished.

In accordance with application Serial No. 184,161, filed September 11, 1950, now Patent No. 2,639,770 dated May 26, 1953, by Theodore A. Huber proposed to solve the problem of providing elfective firing power to perforate casing with an assembly which is run into and out of thewell through tubing by arranging the guns in their carriage or gun body on trunnions and by providing means for rotating them from the vertical positions which they occupy while being lowered into the well, into horizontal firing positions. Inasmuch as the guns may be tired by electricity, Huber proposed to employ an electric motor to rotate them exactly the right amount.

In accordance with the present invention, it is proposed to provide a perforating gun which can be run into the well through tubing and fired without the use of any electric circuit. Due to the use of a flexible carrier, the diameter of the gun can be as large, or nearly as large as the internal diameter of the tubing and, if necessary, the gun can be pumped down through the tubing. In

some embodiments of the invention hydraulic means is used to fire the gun. By causing the gun to come to rest a predetermined distance below the tubing, it can be positioned accurately in the casing and it can be raised and lowered by moving the tubing.

The objects of the invention will be apparent from the following description, taken in connection with the accompanying drawings, in which:

Fig. 1 is a view in vertical cross-section of casing and tubing in a well bore with a gun constructed in accordance with the present invention being lowered therethrough on a measuring line.

Fig. 2 is a view in vertical cross-section of the gun of Fig. 1.

Fig. 3 is a transverse cross-sectional view of the housing of the gun of Figs. 1 and 2.

Fig. 4 is a view in vertical cross-section of tubing and casing in a well bore with a gun constructed in accordance with another embodiment of the invention located therein.

Fig. 5 is an enlarged fragmentary view of the gun of r Fig. 4, a portion being cut away to show the internal construction of the firing system.

Fig. 6 is an enlarged fragmentary view in quarter crosssection of a gun head like that used in the gun of Fig. 4 but incorporating different means for firing.

Fig. 7 is a fragmentary perspective view of a metal housing for guns like those shown in Figs. 1 and 4.

Referring to the drawing in detail, and first to the embodiment of the invention shown in Figs. 1, 2 and 3, it will be seen that an oil well casing is there shown at 12. A tubing 13 is positioned in the well with its lower end above the portion of the casing which is to be perforated, as shown in Fig. 1.

Within the well as a housing or carriage 14 which is being lowered on a measuring line 15. This carriage may be made of thin steel, like stove pipe, or of rubber, plastic or neoprene hose, as shown, and it is of cylindrical shape. If made of rubber, neoprene or plastic, it may be reenforced by steel wires as shown at 16 in Fig. 3. If made of thin metal, it may be corrugated, in whole or in part, as shown at 14 as in Fig. 7 to increase its flexibility about its longitudinal axis.

To position the gun accurately with respect to the tubing 13, a locator 17 may be secured to the measuring line and a seat 18 provided at the bottom of the tubing. By adjusting the position of the locator on the measuring line before the assembly is run into the well, the desired location may be attained. However, since it is desirable to make the gun as large in diameter as possible to give it adequate fire power, the locator and its seat may be dispensed with so that the gun can have practically as large a diameter as the inside diameter of the tubing, in which case, the measuring line alone can be used to bring the gun to its desired position for perforating.

Within the housing 14, as shown in Fig. 2, there are a number of shaped charges of explosive designated 20. These are confined in a metallic container or envelope 21 which has a conical or other shaped face 22 on one side to cause jet action of the explosion in accordance with well known practices. A cap 23, the shape of a segment of a cylinder having curvature like that of the housing 14, is mounted over the face 22 and a flange 24 thereof is sealed to the envelope 21. The purpose of the cap 23 is to prevent hydraulic pressure from modifying the shape of the face 22 and provide at least sulficient stand-off distance between the face 22 and the casing 12 when the explosion occurs. The charges may be fired by primer cord 25, the upper end of which is in a powder chamber 26, in the conventional manner.

The charges 20 may be staggered, as to their direction of firing, in any desired way. As shown in Fig. 2, adja cent charges fire in directions 90 degrees apart. Since one side of the gun will ordinarily be in contact with the casing, the hole seldom being exactly vertical, some of the caps 23 will be located very close to the casing 12.

As indicated above, the gun, particularly near the charges 20, should have high weight or mass. To this end, inert filling material such as pulverized barytes, lead pellets, sand or the like is packed around the envelopes 21 and the outer rim of the caps 23, as shown at 27. Pulverized or granular material is preferable to solid or larger sizes of material because it will have less tendency to create a shock on the casing, which would tend to burst it. The explosive force is not temporarily confined and then permitted to escape rapidly, as in the case where a mass of concrete is placed around the charge and caused to burst. Moreover, solid material for providing mass would tend to destroy the flexibility of the carriage.

One purpose using a thin metal or plastic housing is to give the gun a certain amount of flexibility so that it can have a large diameter and still pass down through crooked tubing. Liquid, such as mercury, could be used to add weight to the gun but it is expensive. liquids, such as oil, water or mud could be used if precautions are taken to enclose the primer cord 25 properly, but of course their specific gravity is not as high as the materials mentioned.

As the housing 14 is lowered through mud or other liquid in the well bore, the hydrostatic pressure will cause it to deform slightly, but if it is filled with material of the kind indicated, the deformation will be slight and sufiicient flexibility will remain to permit it to pass around bends in the tubing.

When the charges 20 are fired, the jets will perforate the caps 23, the casing 12 and the cement and earth formations around the casing 12. It is known that only a part of the forces created by the explosion of shaped charges are expended in the jet, however. The charges, and in this case the envelopes 21, blow up radially in all directions. The housing 14 is purposely designed so as not to withstand these radial forces. It is intended that it readily blow up and .permit the Weighting material 27 t0 Ordinary scatter in all directions. If the mass of the particles of material 27 is high their acceleration will not be sufficient to cause them to harm the casing appreciably and they will assist in dissipating the shock which tends to burst the casing.

The gun of Fig. 4 may be like that of Figs. 1 and 2 except that it is not lowered into the well bore on a measuring line. This gun is designed to be pumped down the tubing 13. To this end swab cups 28 are mounted as shown on the bottom of the flexible housing 1? and the locator 29 is fixed to the top of the housing 14. A fishing spear 30 is attached to the top of the locator 29 to which a fishing tool may be attached to retrieve the locator 29 and whatever part of the housing 14 remains after the explosion. it is also possible, with an arrangement like that in Fig. 4, to pump the gun on out below the tubing 13 after it has fired, the locator seat being provided with a shear pin 31. If the firing system of Fig. 6 is employed, the pin 31 may be dcsigned to withstand suucient pressure to permit operation of the firing system but then shear to drop the gun and cat 13 to the bottom of the hole.

If desired, the gun of the present invention could be lowered into the well bore on an electric cable and the charges 20 fired electrically. An electric cable is not necessary, however, and three different Ways of firing without the use of such a cable are illustrated in the drawing.

As shown in Fig. 2, the upper part of the housing 14 may be provided with a strong steel section 32 which contains the powder 26 for igniting the primer cord. A conventional percussion firing cap 33, like that used in small arms ammunition, may be used to fire the powder 26.

in accordance with the present invention the firing may be controlled by regulating the hydraulic pressure in the well bore. To this end, a firing pin 34 may be positioned above the firing cap 33. It may be mounted on a piston 35 or other means for maintaining a fluid t ght seal with the cylinder 36 of the section 32 and held against downward movement until ready for a shear pin 37. A hollow coupling 38 having ports 39 may connect the measuring line 15 to the section 32.

When the gun of Fig. 2 is to be fired, it is held in position by the measuring line 15, with or without the locator 17 and the hydrostatic pressure in the well is increased, as by exerting pump pressure at the surface of the ground. When the pressure exceeds the predetermined amount for which the shear pin 37 is designed, the pin shears and the piston 35 moves down to cause the firing pin 34 to strike the cap 33 and set off the powder 26.

In Fig. 5, the section 32 is provided with a solid head 40 and a clock firing assembly 41 is employed to control the firing. The powder 26 may be fired by an electric spark and the assembly 41 may contain a battery, an induction etc., the circuit of which is closed and opened by the clock after the gun has been lowered into position a predetermined length of time to cause the spark to jump.

In Fig. 6 a hydraulically operated system using differ ential pressure is illustrated. in Fig. 2, the total fluid pressure is used to move the piston 35. This has a disadvantage in that different wells may require the use of shear pins of dilerent strength. if the arrangement of Fig. 6 is employed, all shear pins may be alike.

The head 42 of Fig. 6 is hollow and has ports therein above the tapered portion 44 which comes in contact with the seat 18 in the bottom of tubing 13. Unlike the arrangement of Fig. l and that of Fig. 5, this head 42 is intended to maintain a fluid tight seal with the seat 18 in the casing. The piston 35 is rnount ed :in a cylinder 36 and held by a shear pin 3'7, as in the arrangement of Fig. 2, but a small port 45 is drilled in the cylinder 36 beneath the piston When the gun is to be fired, after being brought into position with the head 42 on the seat 18 of the tubing 13, by exerting pump pressure or the like Wihin the tubing 13, the piston 35 is caused to move and the firing pin 34 caused to strike the firing cap 33, Except when the gun is in position no pressure can be exerted hydraulically across the piston 35 and there is little danger of the gun firing when not at the desired location in the well bore. If the gun is pumped down through the tubing 13 under the action of the swab cups 28 of Fig. 4, it will fire automatically when the head 42 comes to rest on the seat 18.

While only a few embodiments have been shown and described herein, it is obvious that various changes may be made without departing from the spirit of the invention or the scope of the annexed claims.

I claim:

1. In a gun for perforating casing in oil wells or the like, in combination, a flexible elongated carriage small enough in diameter to be run into the well through tubing inside the casing to be perforated, said carriage including a flexible outer tubular container, a plurality of shaped charges of explosive transversely mounted in spaced relation in said container, at pressure resistant envelope enclosing and sealing each shaped charge and a body of unconsolidated filling material composed of solid granules in the container around the shaped charges, said outer tubular container being designed to be substantially destroyed by the explosion of said shaped charges.

2. The arrangement defined in claim 1, in combination with sealing means disposed on the exterior of said carriage and adapted to form a seal to the passage of fluids downwardly past said carriage when said carriage is within said tubing.

References Cited in the file of this patent UNITED STATES PATENTS 122,654 Roberts Jan. 9, 1872 316,137 Gallagher Apr. 21, 1885 1,298,500 Hardel Mar. 25, 1919 1,541,790 Cheley et al. June 16, 1925 1,641,483 Greene Sept. 6, 1927 2,058,287 Anderson Oct. 20, 1936 2,307,360 Collins Jan. 5, 1943 2,436,036 Defenbaugh Feb. 17, 1948 2,494,256 Muskat et al. Jan. 10, 1950 2,453,814 Thompson et al. Mar. 6, 1951 2,577,625 Page Dec. 4, 1951 2,669,928 Sweetman Feb. 23, 1954 

1. IN A GUN FOR PERFORATING CASING IN OIL WELLS OR THE LIKE, IN COMBINATION, A FLEXIBLE ELONGATED CARRIAGE SMALL ENOUGH IN DIAMETER TO BE RUN INTO THE WELL THROUGH TUBING INSIDE THE CASING TO BE PERFORATED, SAID CARRIAGE INCLUDING A FLEXIBLE OUTER TUBULAR CONTAINER, A PLURALITY OF SHAPED CHARGES OF EXPLOSIVE TRANSVERSELY MOUNTED IN SPACED RELATION IN SAID CONTAINER, A PRESSURE RESISTANT ENVELOPE ENCLOSING AND SEALING EACH SHAPED CHARGE AND A BODY OF UNCONSOLIDATED FILLING MATERIAL COMPOSED OF SOLID GRANULES IN THE CONTAINER AROUND THE SHAPED CHARGES, SAID OUTER TUBULAR CONTAINER BEING DESIGNED TO BE SUBSTANTIALLY DESTROYED BY THE EXPLOSION OF SAID SHAPED CHARGES. 